1. Field of the Invention
This invention relates to a novel diphenol compound and to a novel aromatic polycarbonate resin containing diol units from the diphenol compound. The present invention is also directed to an electrophotographic photoconductor having an electroconductive support and a photoconductive layer formed thereon and containing the above aromatic polycarbonate resin which has charge transporting properties.
2. Description of Prior Art
Recently organic photoconductors (OPC) are used in many copying machines and printers. The organic photoconductor has a layered structure comprising a charge generation layer (CGL) and a charge transport layer (CTL) which are successively overlaid on an electroconductive support. The charge transport layer (CTL) is a film-shaped layer comprising a binder resin and a low-molecular-weight charge transport material (CTM) dissolved therein. The addition of such a low-molecular-weight charge transport material (CTM) to the binder resin lowers the intrinsic mechanical strength of the binder resin, so that the CTL film is fragile and has a low tensile strength. Such lowering of the mechanical strength of the CTL causes the wearing of the photoconductor or forms scratches and cracks on the surface of the photoconductor.
Although some vinyl polymers such as polyvinyl anthracene, polyvinyl pyrene and poly-N-vinylcarbazole have been studied as high-molecular-weight photoconductive materials for forming a charge transporting complex for use in the conventional organic photoconductor, such polymers are not satisfactory from the viewpoint of photosensitivity.
In addition, high-molecular-weight materials having charge transporting properties have been also studied to eliminate the shortcomings of the above-mentioned layered photoconductor. For instance, there are proposed an acrylic resin having a triphenylamine structure as reported by M. Stolka et al., in xe2x80x9cJ. Polym. Sci., vol 21, 969 (1983)xe2x80x9d; a vinyl polymer having a hydrazone structure as described in xe2x80x9cJapan Hard Copy ""89 p. 67xe2x80x9d; an aromatic polycarbonate resin having a benzidine structure as disclosed in Japanese Laid-Open Patent Application 64-9964; and polycarbonate resins having a triarylamine structure as disclosed in U.S. Pat. Nos. 4,801,517, 4,806,443, 4,806,444, 4,937,165, 4,959,288, 5,030,532, 5,034,296, and 5,080,989, and Japanese Laid-Open Patent Applications Nos. 64-9964, 3-221522, 2-304456, 4-11627, 4-175337, 4-18371, 4-31404, and 4-133065. However, any materials have not yet been put to practical use.
According to the report of xe2x80x9cPhysical Review B46 6705 (1992)xe2x80x9d by M. A. Abkowitz et al., it is confirmed that the drift mobility of a high-molecular weight charge transport material is lower than that of a low-molecular weight material by one figure. This report is based on the comparison between the photoconductor containing a low-molecular weight tetraarylbenzidine derivative dispersed in the photoconductive layer and the one containing a high-molecular polycarbonate having a tetraarylbenzidine-containing skeleton in its molecule and suggests that the photoconductor employing the high-molecular weight charge transport material produces poor results in terms of the photosensitivity and the residual potential although the mechanical strength of the photoconductor is improved.
The reason for poor results in the photosensitivity and the residual potential caused by use of the high-molecular weight charge transport material has not yet been clarified. It is, however, inferred that, in a polycarbonate having a tetraarylbenzidine-containing skeleton, the presence of electron-attracting carbonyloxy groups and electron-donating tertiary amino groups on the aryl groups causes localization of electrons, which adversely affects the hole transfer.
In accordance with one aspect of the present invention there is provided a diphenol compound comprising: at least one triarylamine group, two divalent alkane groups each having two, first and second bonds, said first bond of each of said alkane groups being bonded to respective one of the aryl groups of said at least one triarylamine group, an aryl group bonded to the second bond of each of said two alkane groups, and a hydroxyl group bonded to the aryl group linked to each of said two alkane groups.
In another aspect, the present invention provides a diphenol compound represented by the following formula (1): 
wherein Ar1, Ar2, Ar4 and Ar5 stand, independently from each other, for an arylene group or a substituted arylene group, Ar3 stands for an aryl group or a substituted aryl group, Z stands for an arylene group or xe2x80x94Ar6xe2x80x94Zaxe2x80x94Ar6xe2x80x94 where Ar6 represents an arylene group or a substituted arylene group and Za represents xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or an alkylene group, R and Rxe2x80x2 stand, independently from each other, for a straight chain alkylene group or a branched alkylene group and n is an integer of 0 or 1.
The present invention also provides an aromatic polycarbonate resin comprising a main structural unit represented by the following formula (3): 
wherein Ar1, Ar2, Ar4 and Ar5 stand, independently from each other, for an arylene group or a substituted arylene group, Ar3 stands for an aryl group or a substituted aryl group, Z stands for an arylene group or xe2x80x94Ar6xe2x80x94Zaxe2x80x94Ar6xe2x80x94 where Ar6 represents an arylene group or a substituted arylene group and Za represents xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or an alkylene group, R and Rxe2x80x2 stand, independently from each other, for a straight chain alkylene group or a branched alkylene group and n is an integer of 0 or 1.
The present invention further provides a polycarbonate resin comprising a recurring unit represented by the following formula (6): 
wherein Ra, Rb, Rc and Rd stand for an alkyl group, Ar3 stands for an aryl group or a substituted aryl group, Z stands for an arylene group or xe2x80x94Ar6xe2x80x94Zaxe2x80x94Ar6xe2x80x94 where Ar6 represents an arylene group or a substituted arylene group and Za represents xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or an alkylene group, R and Rxe2x80x2 stand, independently from each other, for a straight chain alkylene group or a branched alkylene group, n is an integer of 0 or 1 and X stands for a group selected from the group consisting of divalent aliphatic groups, substituted divalent aliphatic groups, divalent alicyclic groups, substituted divalent alicyclic groups, divalent aromatic groups, substituted divalent aromatic groups, divalent groups obtained by linking at least two of the foregoing groups and groups represented by the following formulas: 
wherein R1, R2, R3 and R4 stand, independently from each other, for an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group or a halogen atom, a and b are independently an integer of 0-4, c and d are independently an integer of 0-3, Y is selected from the group consisting of a direct bond, straight chain alkylene groups having 2-12 carbon atoms, substituted straight chain alkylene groups having 2-12 carbon atoms, branched A chain alkylene groups having 3-12 carbon atoms, substituted branched chain alkylene groups having 3-12 carbon atoms, divalent groups composed of at least one alkylene group having 1-10 carbon atoms and at least one xe2x80x94Oxe2x80x94 or at least one xe2x80x94Sxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94 and groups represented by the following formulas: 
wherein Z1 and Z2 stand independently from each other for a divalent aliphatic group, a substituted divalent aliphatic group, an arylene group or a substituted arylene group; R51 R6 and R12 stand independently from each other for a halogen atom, an alkyl group, a substituted alkyl group, an alkoxyl group, a substituted alkoxyl group, an aryl group or a substituted aryl group, R7, R8, R9, R10 and R11 stand independently from each other for a hydrogen atom, R6 and R7 may form a carbocyclic ring having 5 to 12 carbon atoms together, R13 and R14 stand independently from each other for a direct bond or an alkylene group having 1-4 carbon atoms, R15 and R16 stand independently from each other an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group, e and g are each an integer of 0-4, f is an integer of 1 or 2, h is an integer of 0-20 and i is an integer of 0-2000.
The present invention further provides an electrographic photoconductor comprising an electroconductive support, and a photoconductive layer provided on said support and containing an aromatic polycarbonate resin including at least one triarylamine group, two divalent alkane groups each having two, first and second bonds, said first bond of each of said alkane groups being bonded to respective one of the aryl groups of said at least one triarylamine group, an aryl group bonded to the second bond of each of said two alkane groups, a xe2x80x94Oxe2x80x94 group bonded to the aryl group of one of said two alkane groups to form an arylxe2x80x94Oxe2x80x94 group, and an oxycarbonyl group xe2x80x94Oxe2x80x94COxe2x80x94 bonded to the aryl group of the other one of said two alkane groups to form aryl xe2x80x94Oxe2x80x94COxe2x80x94 group.
The present invention further provides an electrographic photoconductor comprising an electroconductive support, and a photoconductive layer provided on said support and containing an aromatic polycarbonate resin comprising a main structural unit represented by the following formula (3): 
wherein Ar1, Ar2, Ar4 and Ar5 stand, independently from each other, for an arylene group or a substituted arylene group, Ar3 stands for an aryl group or a substituted aryl group, Z stands for an arylene group or xe2x80x94Ar6xe2x80x94Zaxe2x80x94Ar6xe2x80x94 where Ar6 represents an arylene group or a substituted arylene group and Za represents xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or an alkylene group, R and Rxe2x80x2 stand, independently from each other, for a straight chain alkylene group or a branched alkylene group and n is an integer of 0 or 1.
The present invention further provides an electrographic photoconductor comprising an electroconductive support, and a photoconductive layer provided on said support and comprising a polycarbonate resin having a recurring unit represented by the following formula (6): 
wherein Ra, Rb, Rc and Rd stand for an alkyl group, Ar3 stands for an aryl group or a substituted aryl group, Z stands for an arylene group or xe2x80x94Ar6xe2x80x94Zaxe2x80x94Ar6xe2x80x94 where Ar6 represents an arylene group or a substituted arylene group and Za represents xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or an alkylene group, R and Rxe2x80x2 stand, independently from each other, for a straight chain alkylene group or a branched alkylene group, n is an integer of 0 or 1 and X stands for a group selected from the group consisting of divalent aliphatic groups, substituted divalent aliphatic groups, divalent alicyclic groups, substituted divalent alicyclic groups, divalent aromatic groups, substituted divalent aromatic groups, divalent groups obtained by linking at least two of the foregoing groups and groups represented by the following formulas: 
wherein R1, R2, R3 and R4 stand, independently from each other, for an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group or a halogen atom, a and b are independently an integer of 0-4, c and d are independently an ingeger of 0-3, Y is selected from the group consisting of a direct bond, straight chain alkylene groups having 2-12 carbon atoms, substituted straight chain alkylene groups having 2-12 carbon atoms, branched chain alkylene groups having 3-12 carbon atoms, substituted branched chain alkylene groups having 3-12 carbon atoms, divalent groups composed of at least one alkylene group having 1-10 carbon atoms and at least one xe2x80x94Oxe2x80x94 or at least one xe2x80x94Sxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94 and groups represented by the following formulas: 
wherein Z1 and Z2 stand independently from each other for a divalent aliphatic group, a substituted divalent aliphatic group, an arylene group or a substituted arylene group; R5, R6 and R12 stand independently from each other for a halogen atom, an alkyl group, a substituted alkyl group, an alkoxyl group, a substituted alkoxyl group, an aryl group or a substituted aryl group, R7, R8, R9, R10 and R11 stand independently from each other for a hydrogen atom, R6 and R7 may form a carbocyclic ring having 5 to 12 carbon atoms together, R13 and R14 stand independently from each other for a direct bond or an alkylene group having 1-4 carbon atoms, R15 and R16 stand independently from each other an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group, e and g are each an integer of 0-4, f is an integer of 1 or 2, h is an integer of 0-20 and i is an integer of 0-2000.
When the above polycarbonate resin according to the present invention is used in a photoconductive layer, problems of the conventional photoconductor in mechanical properties and in electrical properties can be solved. Although not wishing to be bound by the theory, it is presumed that the presence of the aryl-substituted alkane groups through which oxycarbonyl groups of the polycarbonate resin are linked to the aryl groups of the triarylamines can prevent the localization of electrons so that the motion of molecules can be facilitated.
It is an object of the present invention to provide a novel diphenol compound which is useful for producing a novel polycarbonate.
Another object of the present invention is to provide a novel polycarbonate useful as a charge-transporting material for a photoconductive layer of an electrophotographic photoconductor.
It is a further object of the present invention to provide an electrophotographic photoconductor having good mechanical properties as well as good electrical and optical properties such as high photosensitivity and low residual potential.